Donna Lieberman, the executive director for the New York Civil Liberties Union, is being sued by a former staffer who claims he was fired for his sexual orientation.Daniel Shapiro

The head of the ultra-liberal New York Civil Liberties Union is a bigot, according to a new lawsuit by a former staffer who claims he was fired for being gay.

Kerry Watterson, former head of development at NYCLU, says in a Manhattan Supreme Court suit that the organization’s executive director, Donna Lieberman, “harassed and mistreated him” with anti-gay gibes.

The 39-year-old Jersey City resident says Lieberman, a prominent civil- rights attorney, singled him out as the only gay man on the senior staff with jokes about his sexual orientation — and then had him fired when he complained to the board.

In one alleged incident during a staff meeting in July 2013, Lieberman discussed an agenda item titled “Swag and Fees,” referring to goody bags available for guests at an upcoming benefit concert.

But she pronounced the item as “fags and swees” while glaring at Watterson, the suit says.

Lieberman even “looked around the room for approving laughter,” according to court papers.

Watterson was “deeply offended and humiliated by this discriminatory comment,” the suit says.

The University of Arizona grad was terminated in October 2013 for “poor work performance.” He pointed out in court papers, however, that he raised more than $1 million during his two years on the job.

A NYCLU spokeswoman said, “The State Division of Human Rights had an ample opportunity to consider Mr. Watterson’s claims and properly rejected those claims.”

The Human Rights division ruled in a Feb. 5, 2015, decision that there is “no probable cause to believe that [the NYCLU] has engaged in the unlawful discriminatory practice complained of.”

Watterson’s attorney, Christopher Riano, declined to respond to the ruling.

Watterson’s suit against the NYCLU, Lieberman and the Division of Human Rights asks the court to force the agency to reconsider his claims in a full administrative hearing.